An inspection method using a light-section method as illustrated in FIG. 5 is conventionally known as an inspection method for determining the acceptability of the shape of a tire side. In such an inspection method, a tire 50 to be inspected is mounted on a rotating unit 61 and rotated with its axis as the axis of rotation. At the same time, a slit light is cast to the side (tire side) 50K of the tire 50 by a light casting unit 62 using semiconductor laser or the like, and slit images of the side 50K are shot by an area camera 63 such as a CCD camera. Then the shape of the side 50K is derived from the image data (luminance data) of the slit images S, and the acceptability of the shape is determined by comparing it against a reference image (inspection image) of the side of a tire. To be more specific, the center coordinates of the pixels bright with light, out of the image data of the slit images S, are calculated, and the two-dimensional coordinates of the slit images S are calculated. Then the two-dimensional coordinates are converted into three-dimensional coordinates using the positional relationship between the casting angle of the slit light and the shooting angle of the slit image S and the angle of rotation of the tire 50 detected by a rotation angle detecting unit 64, and in this way the contour (external form) and unevenness along the vertical tire cross section of the side 50K of the tire 50 is detected. Then the acceptability of the shape of the tire 50 is determined by comparing the detected image of the side 50K against the reference image of the tire side (see Reference 1, for instance).    Reference 1: Japanese Unexamined Patent Application Publication No. 11-138654